I'll guess its the high ph, first. Most aquatic plants evolved to
thrive in lowland waters which are usually between 5.5ph and 7ph

A simple test would be to set a bucket of pond water aside, adjust the
ph by adding something measurably acid for example peat, crank the ph
down to 7ph and sit back and see if it works... If the water hyacinth
appears to thrive significantly better a week later, consider topping
up your pond with rain water from your roof, rather than the usual
hard water, or get used to the idea that your hard water is limiting
what aquatic plants you can grow...

Regards, andy
http://www.members.aol.com/abdavisnc/swglist.html
(andys aquatic plant list for interesting swaps


I assume water lilies are like other plants and produce more blooms if dead
headed. That's swell for ones I can easily reach, but does anyone have a
handy tool or solution for the ones I have to get into the pond to clip?

Is it the ph? A lack of nutrients? I have a couple of large filters so
no ammonia or nitirite. Salt? I tried potash and koi clay no luck
there either. Any ideas?

thanks